The heart of a computer is a magnetic disk drive that includes a magnetic disk, a slider where a magnetic head assembly including write and read heads is mounted, a suspension arm, and an actuator arm. When the magnetic disk is stationary, the slider is biased by the suspension arm into contact with the surface of the magnetic disk. When the magnetic disk rotates, the rotating magnetic disk swirls air at an air bearing surface (ABS) of the slider, causing the slider to fly on an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk, where signal fields are written and read by the write and read heads, respectively. The write and read heads are connected to processing circuitry that operates according to a computer program to implement write and read functions.
An exemplary high performance read head employs a read element for sensing the signal fields from the rotating magnetic disk. The most recently explored read element, a giant magnetoresistance (GMR) sensor, comprises a nonmagnetic Ni—Cr—Fe seed layer, ferromagnetic Ni—Fe/Co—Fe sense layers, a nonmagnetic Cu—O spacer layer, a ferromagnetic Co—Fe reference layer, a nonmagnetic Ru antiparallel (AP) exchange-coupling layer, a ferromagnetic Co—Fe keeper layer, and nonmagnetic Cu and Ta cap layers. Crystalline reconstruction occurring in the Ni—Cr—Fe seed and Ni—Fe sense layers causes the two layers to behave as if a monolayer film exhibiting coarse polycrystalline grains with a strong <111> texture, thus leading the GMR sensor to exhibit low sensor resistance and a high GMR coefficient. Intrinsic and extrinsic uniaxial anisotropies of the Co—Fe reference and Co—Fe keeper layers, and their ferromagnetic/ferromagnetic AP exchange coupling occurring across the Ru AP exchange-coupling layer cause the Co—Fe reference and Co—Fe keeper layers to be self-pinned, thus leading the GMR sensor to operate properly. Alternatively, an antiferromagnetic Pt—Mn pinning layer is sandwiched into the Co—Fe keeper and Cu cap layers. Ferromagnetci/antiferromagnetic exchange coupling occurring between the Co—Fe keeper and Pt—Mn pinning layers causes rigid pinning to the Co—Fe keeper layer, thus reinforcing the AP exchange coupling pinning and ensuring the proper sensor operation.
In the prior art, the fabrication process of the magnetic head assembly typically includes building the read head on a wafer, building the write head on the wafer, slicing the wafer into rows, mechanically lapping and overcoating the rows, and slicing the rows into sliders. During building the read head on the wafer, the GMR sensor is formed with three photolithographic patterning steps. FIG. 1 illustrates a top view of a GMR sensor 100 formed according to the prior art. FIGS. 2 and 3 are cross-sectional views of the GMR sensor 100 formed in the prior art on planes perpendicular and parallel, respectively, to its ABS. In the first step, a region 101 is formed with a height of about 3,000 nm, much larger than the designed height of the GMR sensor 100 (60 nm). An insulating Al2O3 film is deposited outside the region 101. In the second step, two regions 102 are formed with a separation equivalent to the designed width of the GMR sensor 100 (80 nm). Longitudinal bias and first conducting layers are deposited into the two regions 102. In the third step, two regions 103 are formed on top of the two regions 102. Second conducting layers are deposited into the two regions 103.
FIGS. 4 and 5 illustrate cross-sectional views of the GMR sensor formed and a magnetic head assembly fabricated, respectively, in the prior art on a plane perpendicular to its ABS after mechanical lapping and overcoating. During the mechanical lapping, the height of the GMR sensor 100 is reduced from about 3,000 nm to a designed height of as small as 60 nm. The mechanical lapping is monitored by measuring the resistance of an electrical lapping guide (not shown) with the same structure and geometry as the GMR sensor 100, located more than 100 μm away from the GMR sensor 100, and is stopped as its resistance substantially increases from about 16 to about 50 Ω. Hence, in the prior-art, the designed width of the GMR sensor is defined by the photolithographic patterning, while its designed height is defined by the mechanical lapping.
There are several disadvantages in the GMR sensor formed in the prior art. First, electrostatic discharge (ESD) damages may occur during the mechanical lapping due to an unwanted substantial increase in the resistance of the GMR sensor 100. The GMR sensor 100 may thus be not viable at all. Second, the sensor height may substantially vary due to difficulties in remotely controlling the resistance of the GMR sensor 100 within a desired narrow resistance range. A manufacturing control for a high yield may thus be very challenging. Third, the magnetic moments of sense, reference and keeper layers at the ABS may substantially decrease by uncertain amounts, while the pinning layer may corrode, due to the exposure of the ABS to the chemical solution and air. The designed magnetic moments and desired exchange-coupling may not be attained at the ABS, thus substantially reducing the signal sensitivity of the GMR sensor 100. Fourth, all the various layers of the GMR sensor 100 may be recessed differently and an unwanted stepped ABS is formed, due to their different mechanical lapping rates. The protection overcoat 200 may thus not adhere well on this stepped ABS, thus causing concerns on the contact of the GMR sensor 100 with the rotating magnetic disk during sensor operation. Because of these problems, the GMR sensors 100 formed in the prior art may not be suitable for magnetic recording at ultrahigh densities.
What is needed is a method that reduces the risk of ESD damages, controls the sensor resistance, minimizes the losses in the magnetic moments, and eliminates the corrosion.
What is also needed is a method that precisely controls the height of the GMR sensor 100.
What is further needed is a method that eliminates the protection overcoat, thereby minimizing a spacing between the GMR sensor 100 and the rotating magnetic disk.